Rolls such as those employed as roller conveyors for use at high temperature can be made from an inner-metal shaft that has an outer insulating cover of asbestos. In manufacturing the roll, the asbestos can be supplied as annular disks which may be cut from asbestos board. The resulting rolls are usually referred to as asbestos board rolls. The assembly of asbestos disks onto a shaft to form a conveyor roll has been discussed for example in U.S. Pat. No. 3,802,495. These rolls can contain a binder which enhances the hardness and the wear resistance of the rolls. In use, the binder may burn out of the asbestos board rolls. As this occurs, disks separate and the asbestos cover can rotate on the interior shaft over which the disks have been assembled. As a result of this enlargement, the cover is prone to spin on the shaft. In an attempt to overcome this cover spinning, metal rings inserted in the cover with keys were tried with the asbestos board rolls.
It has also been known to place load bearing members, sometimes referred to as "tires" along an insulating roll cover. Such load bearing members have an exterior surface which is typically flush with the outer surface of the roll insulation. Such load bearing members are particularly desirable for providing rolls which have extended outer surface wear in the conveying of heavy loads.
It has also been known that to accommodate thermal expansion of binder-containing fiber roll covers, such covers can be made from fiber subassemblies which are placed on a shaft and separated in placement by separators means. The separators may be structural metallic members or non-structural items such as metal foils. As structural members, the separators may be flanged plates inserted between subassemblies, which subassemblies are composed of a plurality of fiber disks. These separators can provide expansion joints as has been discussed in U.S. Pat. No. 4,352,230.
It has been more recently taught in U.S. Pat. No. 5,205,398 that spacers may be utilized in roller conveyors having thermal insulation of highly compressed ceramic fiber. These spacers, rather than being load bearing members, are typically in foil form and can add flexibility to the covering for the roll.
As the applications for such highly compressed ceramic fiber rolls proliferate, more challenging industrial conditions, including harsh operating environments, are being met. Under these conditions, particularly for rigidized and highly compressed fiber roll covers, it will be desirable to extend the operational life of the cover while obviating failure phenomena, e.g., longitudinal cracking, which can cause premature cover failure. In addition to competitive ruggedness and long-service life, the cover should also exhibit desirable insulating characteristics as well as provide an environmentally appealing product.